Sexually transmitted Chlamydia trachomatis infections in women, often asymptomatic, have serious consequences if left untreated. However, studies from Group Health Cooperative (GHC) have shown the impact can be decreased (i.e., a 56 percent decrease in PID) if at-risk women receive screening and treatment. Over the last two years, GHC has developed an evidence-based chlamydia screening guideline to initiate translation of the evidence into practice. Objective: To evaluate the effectiveness of several multifaceted strategies for guideline implementation. Site: Thirty staff model outpatient clinics at GHC. Methods: This is a randomized trial of guideline implementation strategies carried out at the provider and patient levels. Using a 2x2 factorial design, we will compare standard guideline implementation to three other strategies: one with only provider-specific components, one with only patient-specific components and one with both provider- and patient-specific components. Provider- specific strategies (with randomization occurring at the clinic level) include the use of opinion leaders, measurement and feedback, and prompts placed in Pap test kits. The patient- specific strategy (with randomization of individual enrollees) consists of a prompt placed in the chart of 14-20 year-old females as a paper-based test to establish the case for a future computerized automated prompt system. Outcomes: Outcomes will be measured at baseline and post-implementation. The primary outcome is the rate of appropriate chlamydia screening among 14- 25 year-old females. Other primary outcomes are 1) the rate of chlamydia screening as defined by a new HEDIS measure; 2) changes in provider knowledge, attitudes/beliefs, self-efficacy, practices, and perceived barriers and supports; 3) the cost per woman appropriately screened and the marginal cost-effectiveness of each intervention arm. Secondary outcomes include changes in the rates of positive chlamydia tests, PID and ectopic pregnancy. Major study benefits: To our knowledge this will be the first study to evaluate conceptually-based guideline implementation strategies in a defined HMO clinical population. In order to further enhance generalizability, we will test selected implementation strategies in a network-model managed care setting.